We are seeking to identify new polypeptides coded for by the RNA phages and to locate the genes which code for the new polypeptides. To date we have identified two new proteins, L protein and protein 5. The former is implicated in cell lysis and is coded by a gene which overlaps both the genes for the major coat protein and for the RNA replicase. The latter, the product of a translational frameshift, is a hybrid of coat and L proteins. Using both in vitro translation of phage RNA and analysis of cells infected with mutant phage, we are analyzing the mechanisms by which the translation of the newly-identified cistrons is controlled. Results so far indicate that coat protein must be translated to allow initiation of translation of L protein. Additional experiments include determination of the intracellular location of phage-coded proteins and selection of new phage mutants.